From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5691B4756C5; Tue, 1 Sep 2026 13:13:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788268418; cv=none; b=HxgdzaVDe8n5GhgsucNCX9Ip+UrnKCTp0xkI4QoJi4Ycif4tPtExoALxX8jFJb5GAgM9weRJPleFANhLosGSvztle5pGIZh2qM3kt/3cpnLZ8/mEiFY1ApkPjw8m73MWzdp7VsqbHVBm/PGL2ieuxj8+MDkt4wL3aLoOE8WIHb8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788268418; c=relaxed/simple; bh=lZqnF/fq0s75WPlK1Ldiv9o028oS83xr/Lv60UdZAxc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FZ75xTi9vZ3lcStaNwiPc+7E4Sc+yYN/lmjxVgEOux5inZYdiZHkyJoI2oM8Y3rYiAzaL4t7auXZ7zlJ2tFcRPdewHMKTV+w/weE+NgomJHpVoialSVegZt/IMotSAuppFR6kRhyGQWWbRduXRoNy/Rr5so7ibMuarw/FnLVWu0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e7aBuYx/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="e7aBuYx/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8A4F1F00A3D; Tue, 1 Sep 2026 13:13:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788268417; bh=/E3Oie88We+VUNBoQinHbEvxciAXpLnuOmC5tKc4/XE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=e7aBuYx/zoaNFKLfyEi3UwnDYq4cH2lGtZXVK8S2AnTXEpjIkTxPvQPvbnSKGBfCE n+3ROEh/GlRyDbtHcq8cp9T2dv9o+stRSkAbb9/rXv1D02xuuuaRI3FjNcDA63olqM +f9pWQPDebd/5u3QrrvNqgVNHMvS/aGO+8a6Bnt6f5wBvuFy3QoKbraB8D/HcNnQMd uE3raa2cOTxCpXZDsVTb90cy+Wqql3A8KH42Q1xeIFfoIGLwnubw/p37bcVoUiMKf0 hbcuRernukzJBG6qSveIbRz9sujbYxISeQMTsBRVr1JQPkhXSGrVH+DWGztzhJ/Ozn umezALzzlzjwA== From: SJ Park To: Andrew Morton Cc: SJ Park , stable@vger.kernel.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 6/7] mm/damon/core: handle extreme memory state in get_node_memcg_used_bp() Date: Tue, 1 Sep 2026 06:13:23 -0700 Message-ID: <20260901131326.97615-7-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260901131326.97615-1-sj@kernel.org> References: <20260901131326.97615-1-sj@kernel.org> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In extreme unlikely situations, total memory might be zero. In less extreme but still very unlikely situations, lruvec_page_state() calls might let the caller show used memory larger than total memory. In the two cases, damos_get_node_memcg_used_bp() could cause division by zero, or return underflowed value, respectively. Handle the cases by respectively returning 100% and 0% for used and free memory queries in the corner cases. This issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260329154813.47382-1-sj@kernel.org Fixes: b74a120bcf50 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP") Cc: # 6.19.x Signed-off-by: SJ Park --- mm/damon/core.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index ad3657d356fbc..3060edf5e4fa6 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2854,6 +2854,12 @@ static unsigned long damos_get_node_memcg_used_bp( mem_cgroup_put(memcg); si_meminfo_node(&i, goal->nid); + if (!i.totalram || i.totalram < used_pages) { + if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) + return 10000; + else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ + return 0; + } if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) numerator = used_pages; else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ -- 2.47.3